When I was 4/5 I was going to have two children called [name]Lucy[/name] and [name]Tom[/name] when I grew up
hehe. Unfortunately a couple of [name]Lucy[/name]'s I’ve met have given me bad associations with the name (don’t you hate that!) and it’s too popular for my tastes, but I can definitely see why you love it! It’s so sweet on a little girl but one of my main reservations used to be that it wouldn’t age well, but one of my best friend’s fiancee is called [name]Lucy[/name] and is in her 20s and it sounds great on her!
So, on to [name]Lucy[/name]'s “sisters” 
[name]Eliza[/name] - I do agree this works really well with [name]Lucy[/name]. [name]Both[/name] have a kind of perky, wholesome, fun feel to me. I’d keep it on the list for now while you decide if you really love it, but if you decide you don’t I’d nix it. I think it’s more important to love each individual name than the sibset.
[name]Norah[/name] - I prefer the [name]Nora[/name] spelling but either way I think it’s a really sweet and gentle name, which are qualities I also see in [name]Lucy[/name]. I don’t think it’s plain at all! [name]Lucy[/name] and [name]Nora[/name] sounds adorable. Or even [name]Lucinda[/name] and [name]Eleanor[/name], nn [name]Lucy[/name] and [name]Nora[/name]? Or [name]Luciana[/name] and [name]Eleonora[/name] nn [name]Lucy[/name] and [name]Nora[/name]?
[name]Ramona[/name] - I love [name]Ramona[/name], but to me it’s like the total opposite kind of name to [name]Lucy[/name] so I wouldn’t use them together. [name]Ramona[/name]'s so strong, quirky and a little masculine to me. [name]Lucy[/name] is sweet, soft and feminine.
[name]Delia[/name] - I prefer [name]Cordelia[/name], but [name]Delia[/name] sounds better with [name]Lucy[/name]. [name]Lucy[/name] and [name]Delia[/name]. Yup, adorable!
[name]Cordelia[/name] would work well with a longer version of [name]Lucy[/name] like [name]Lucienne[/name] or [name]Lucinda[/name] though?
[name]Claire[/name] - if you’ve always wished you were a [name]Claire[/name] I think that’s pretty much the highest compliment you could pay a name, and I happen to think [name]Lucy[/name] and [name]Claire[/name] sound perfect together! [name]Clara[/name]'s cute and vintage but I prefer the fresh sounding [name]Claire[/name] with [name]Lucy[/name].
[name]Matilda[/name] - yes [name]Lucy[/name] and [name]Matilda[/name], or [name]Lucy[/name] and [name]Tilly[/name] are adorable together! I really love the name [name]Matilda[/name] and it has the same warm feel as [name]Lucy[/name] to me. This is a definite yes!
[name]Pearl[/name] - [name]Lucy[/name] and [name]Pearl[/name] just makes me think of the group [name]Lucy[/name] [name]Pearl[/name]!! I actually don’t think the two names match stylistically, but it could make a good middle name for one of the other names?
[name]June[/name] - I love this for the same reason you said! The nn Junebug is so frigging sweet
Unfortunately my partner vetoed it
But for you I love it. [name]Lucy[/name] and [name]June[/name] has a very different feel to [name]Lucy[/name] and [name]Claire[/name] but both work well imo. [name]June[/name] makes [name]Lucy[/name] feel a little more vintage cool.
[name]Fiona[/name] - I don’t see why this couldn’t work with [name]Lucy[/name]. It’s not the most obvious match but I definitely think they could be sisters and [name]Fiona[/name] is a lovely name 
[name]Adelaide[/name] - not my favourite with [name]Lucy[/name], although I do love the name. [name]Lucy[/name] and [name]Adele[/name] on the other hand…perfect! I love that [name]Adele[/name] is such a classic, timeless, simple name, and yet has never been hugely popular. [name]Della[/name] would work as a nn for either [name]Adelaide[/name] or [name]Adele[/name] but I think it’s a more obvious nn for [name]Adele[/name] as the “[name]Dell[/name]” part is more pronounced.
[name]Caroline[/name] - I know the Berries love this name, but to me it’s still just my middle aged aunts name! Lol. And I find it a little boring. [name]Lucy[/name] and [name]Cara[/name] or [name]Lucy[/name] and [name]Cora[/name] would be gorgeous though 
[name]Willa[/name] - I can’t make my mind up with this one. I love [name]Willa[/name], but I’m unsure about [name]Lucy[/name] and [name]Willa[/name]. [name]Willow[/name] seems to me like a better match, but [name]Willa[/name] isn’t bad either I suppose. Something just seems a little off to me when I say the two together.
[name]Olive[/name] - like [name]June[/name], this would make [name]Lucy[/name] seem a lot more vintage and cool, but I don’t like [name]Olive[/name] as much as [name]June[/name], and I don’t like it with [name]Lucy[/name] as much either. [name]Olive[/name] seems like it’s trying a bit too hard to be cool, whereas [name]June[/name] seems like a more natural sister to [name]Lucy[/name].
[name]Ivy[/name] - ahhh [name]Ivy[/name]
This is in my own top 5 names and I really REALLY adore it. I know they have matching “ee” endings, but I still think [name]Lucy[/name] and [name]Ivy[/name] would make super sweet sisters 
[name]Iris[/name] - [name]Iris[/name] might be too delicate to be [name]Lucy[/name]'s sister. [name]Lucy[/name] is soft and sweet but has a bit of spunk, like [name]Ivy[/name] and [name]Eliza[/name] and [name]June[/name], but [name]Iris[/name] is just dainty and soft through and through to me. I do adore the name though so if you love it I’d keep it.
[name]Hazel[/name] - this was my great-aunts name, but I’ve never loved it. I’d use it as a middle name but I don’t love it as a first and it seems harsh next to [name]Lucy[/name] to me.
[name]Flora[/name] - I’m not a fan of [name]Flora[/name]. It seems way too cutesy and [name]Lucy[/name] and [name]Flora[/name] together is just [name]OTT[/name] to me.
So my favourites with [name]Lucy[/name] are; [name]June[/name], [name]Adele[/name], [name]Claire[/name], [name]Matilda[/name], [name]Nora[/name], [name]Eliza[/name], [name]Ivy[/name], [name]Fiona[/name], [name]Delia[/name] and [name]Cara[/name].
I think a lovely sibset would be something like:
[name]Lucy[/name], [name]June[/name], [name]Matilda[/name] and [name]Ivy[/name]
or [name]Lucy[/name], [name]Adele[/name], [name]Claire[/name] and [name]Eliza[/name]
or [name]Lucinda[/name], [name]Adelaide[/name], [name]Cordelia[/name] and [name]Eleanor[/name]
Good luck! 